This invention relates to methods of manufacturing blades of combustion turbine engines and, specifically, to the use of a particular internal core arrangement in the casting of turbine blades, and to a blades having internal cooling configurations formed in this manner.
Conventional combustion turbine engines include a compressor, a combustor, and a turbine. As is well known in the art, air compressed in the compressor is mixed with fuel which is burned in the combustor and expanded in the turbine, thereby rotating the turbine and driving the compressor. The turbine components are subjected to a hostile environment characterized by the extremely high temperatures and pressures of the hot products of combustion that enter the turbine. In order to withstand repetitive thermal cycling in such a hot environment, structural integrity and cooling of the turbine airfoils must be optimized.
As one of ordinary skill in the art will appreciate, serpentine or winding cooling circuits have proven to be an efficient and cost effective means of air cooling the shank and airfoil portions of rotor and stator blades in a combustion turbine engines, and such cooling schemes have become very sophisticated in modern engines. The airfoils typically include intricate internal cooling passages that extend radially within the very thin airfoil. The radial passages are frequently connected by a plurality of small passages to allow the flow of cooling air between the larger flow passages. Fabrication of airfoils with such small internal features necessitates a complicated multi-step casting process.
A problem with the current manufacturing process is the fabrication and maintenance of the cores used in the casting and the low yield rates achieved by conventional processes. The main reason for the low yields is that during the manufacturing process of airfoils, a ceramic core that defines the cooling passages of the airfoil often either breaks or fractures. There are a number of factors that contribute to such a high percentage of ceramic cores becoming damaged. First, ceramic, in general, is a brittle material. Second, the airfoils are very thin and subsequently, the cores are very thin. Finally, the small crossover passages and other intricacies in the airfoil result in narrow delicate features that are easily broken under load.
Another drawback is that the fragile nature of the ceramic cores results in production constraints that limit more optimal cooling schemes. In many instances it may be more advantageous for the airfoil cooling and engine efficiency to have smaller crossover holes or more intricate geometric features. However, more intricate cooling passages are sometimes not practical, since the current manufacturing process already yields an insufficiently small number of usable airfoils and has a high percentage of ceramic cores being damaged. More intricate cooling schemes would result in even lower manufacturing yields and even higher, cost per airfoil. Thus, there is a great need to improve manufacturability of the gas turbine engine airfoils to reduce the cost of each airfoil as well as to improve cooling schemes that accomplish this.